First, a protocol layer model defined in a general broadband wireless access system is described as follows before a Medium Access Control (MAC) header is explained.
FIG. 1 illustrates a protocol layer model defined in a wireless mobile communication system which is based on a generally used IEEE 802.16 system.
Referring to FIG. 1, a MAC layer belonging to a link layer may include three sublayers. A service-specific Convergence Sublayer (CS) may convert or map external network data, which is received through a CS Service Access Point (SAP), into MAC Service Data Units (SDUs) of a MAC Common Part Sublayer (CPS). This layer may have a function to classify SDUs of an external network and to associate each SDU with a corresponding MAC Service Flow IDentifier (SFID) and Connection IDentifier (CID).
The MAC CPS is a layer that provides a core MAC function such as system access, bandwidth allocation, connection setup, and connection management and receives data which is classified by a specific MAC connection from various CSs through the MAC SAP. Here, Quality of Service (QoS) may be applied to scheduling and data transmission through a physical layer.
A security sublayer may provide an authentication function, a secure key exchange function, and an encryption function.
The MAC layer provides a connection-oriented service and is implemented as a transport connection. When a mobile station (MS) is registered in a system, a service flow may be defined by negotiation between the MS and the system. If service requirements change, a new connection may be established. The transport connection defines mapping between peer convergence processes that utilize MAC and a service flow. The service flow defines QoS parameters of a MAC PDU exchanged in a corresponding connection.
A service flow for a transport connection performs a core role in operating the MAC protocol and provides a mechanism for uplink and downlink QoS management. In particular, the service flow may be combined with a bandwidth allocation process.
In a general IEEE 802.16 system, an MS may have a 48-bit universal MAC address per radio interface. This address uniquely defines the radio interface of the MS and may be used to establish a connection with the MS during an initial ranging process. Since a Base Station (BS) verifies MSs using different IDs of the MSs, the universal MAC address may be used as part of an authentication process.
Each connection may be identified by a 16-bit Connection IDentifier (CID). During initialization of an MS, two pairs of management connections (uplink and downlink) are established between the MS and the BS and three pairs including the management connections may optionally be used.
In the above layer structure, transmitting and receiving ends may exchange data and control messages through a Medium Access Control Packet Data Unit (MAC PDU). To generate such a MAC PDU, the BS or MS may incorporate a MAC header into the MAC PDU.
The MS may request an uplink bandwidth by transmitting bandwidth request information in a MAC signaling header format or a MAC subheader format. Here, the MS requests an uplink bandwidth for each connection between the MS and the BS. The following is a description of a general header.
FIG. 2 illustrates an example of a MAC header format used in a wireless MAN mobile communication system which is based on the IEEE 802.16 system. In this specification, one gradation of a block indicating a header structure including the structure of FIG. 2 denotes one bit and one row denotes one byte, and the bits, starting at the top from the Most Significant Bit (MSB) and ending at the bottom with the Least Significant Bit (LSB), are sequentially arranged.
Referring to FIG. 2, six subheaders may be used for a MAC PDU together with a generic MAC header (GMH). Subheaders for each MAC PDU are inserted in the MAC PDU at the rear of the generic MAC header. Each field included in the MAC header is described as follows.
A Header Type (HT) field represents a header type, more particularly represents whether a corresponding MAC PDU includes a generic MAC header, which is followed by a payload in the MAC PDU, or a signaling header for control of bandwidth request (BR) or the like. An Encryption Control (EC) field represents encryption control, more particularly represents whether a payload has been encrypted. A Type field represents the presence or absence of a subheader suffixed to the header and the type of the subheader. An Extended Subheader Field (ESF) field represents the presence or absence of an extended subheader suffixed to the header.
A CRC Indication (CI) field represents whether a CRC is suffixed to the rear of payload. An Encryption Key Sequence (EKS) field represents an encryption key sequence number used for encryption when the payload is encrypted. A length (LEN) field represents the length of the MAC PDU. A CID field represents a connection identifier of a connection for transferring the MAC PDU. A connection is used as an identifier of a MAC layer for data and message transmission between the BS and the MS. A CID is used to identify a specific MS or a specific service between the BS and the MS. A Header Check Sequence (HCS) is used to detect an error in the header. In FIG. 2, a number in parentheses next to each field name represents the number of bits occupied by each field.
FIG. 3 illustrates MAC signaling header type 1 which is used in a wireless MAN mobile communication system which is based on a generally used IEEE 802.16 system.
As shown in FIG. 3, in the signaling header type 1, a header type (HT) field value is set to 1 and an encryption control (EC) field value is set to 0 since the signaling header type 1 is a signaling header. The following Table 1 shows details of the type field.
TABLE 1Type field(3 bits)MAC header type (with HT/EC = 0b10)000BR incremental001BR aggregate010PHY channel report011BR with UL Tx power report100BR and CINR report101BR with UL sleep control110SN Report111CQICH allocation request
As shown in Table 1, a header content field has a different format according to the value of the type field. For example, when the type field has a value of “000” or “001”, the MAC signaling header is used as a Bandwidth Request (BR) header. The format of the header in this case is described below with reference to FIG. 4.
FIG. 4 illustrates an example of a bandwidth request header that is transmitted to a BS when an MS requests a bandwidth in the IEEE 802.16 system.
The following Table 2 shows details of fields included in the bandwidth request header shown in FIG. 4.
TABLE 2LengthName(bits)DescriptionBR19Indicates the size of an uplink bandwidth thatan MS requests for a corresponding CID. Therequest is not affected by physical layermodulation or encoding.CID16Connection IdentifierEC1Set to 0 in a signaling header.HCS8Header Check SequenceHT1Set to 1 since it is a signaling header.Type3Indicates the type of the bandwidth requestheader.
The MS can request up to 512 KB when requesting an uplink bandwidth using the header as shown in FIG. 4.